Association between the DRD2 A1 allele and opium addiction in the Iranian population

Role of antioxidants in the neurobiology of drug addiction: An update

Relationships between protective enzymatic and non-enzymatic pro-antioxidant mechanisms and addictive substances use disorders (SUDs) are analyzed here, based on the results of previous research, as well as on the basis of our current own studies. This review introduces new aspects of comparative analysis of associations of pro-antixidant and neurobiological effects in patients taking psychoactive substances and complements very limited knowledge about relationships with SUDs from different regions, mainly Europe. In view of the few studies on relations between antioxidants and neurobiological processes acting in patients taking psychoactive substances, this review is important from the point of view of showing the state of knowledge, directions of diagnosis and treatment, and further research needed explanation. We found significant correlations between chemical elements, pro-antioxidative mechanisms, and lipoperoxidation in the development of disorders associated with use of addictive substances, therefore elements that show most relations (Pr, Na, Mn, Y, Sc, La, Cr, Al, Ca, Sb, Cd, Pb, As, Hg, Ni) may be significant factors shaping SUDs. The action of pro-antioxidant defense and lipid peroxidation depends on the pro-antioxidative activity of ions. We explain the strongest correlations between Mg and Sb, and lipoperoxidation in addicts, which proves their stimulating effect on lipoperoxidation and on the induction of oxidative stress. We discussed which mechanisms and neurobiological processes change susceptibility to SUDs. The innovation of this review is to show that addicted people have lower activity of dismutases and peroxidases than healthy ones, which indicates disorders of antioxidant system and depletion of enzymes after long-term tolerance of stressors. We explain higher level of catalases, reductases, ceruloplasmin, bilirubin, retinol, α-tocopherol and uric acid of addicts. In view of poorly understood factors affecting addiction, analysis of interactions allows for more effective understanding of pathogenetic mechanisms leading to formation of addiction and development the initiation of directed, more effective treatment (pharmacological, hormonal) and may be helpful in the diagnosis of psychoactive changes.

Single Nucleotide Variants (SNVs) of the Mesocorticolimbic System Associated with Cardiovascular Diseases and Type 2 Diabetes: A Systematic Review

The mesocorticolimbic (MCL) system is crucial in developing risky health behaviors which lead to cardiovascular diseases (CVDs) and type 2 diabetes (T2D). Although there is some knowledge of the MCL system genes linked to CVDs and T2D, a comprehensive list is lacking, underscoring the significance of this review. This systematic review followed PRISMA guidelines and the Cochrane Handbook for Systematic Reviews of Interventions. The PubMed and Web of Science databases were searched intensively for articles related to the MCL system, single nucleotide variants (SNVs, formerly single nucleotide polymorphisms, SNPs), CVDs, T2D, and associated risk factors. Included studies had to involve a genotype with at least one MCL system gene (with an identified SNV) for all participants and the analysis of its link to CVDs, T2D, or associated risk factors. The quality assessment of the included studies was performed using the Q-Genie tool. The VEP and DAVID tools were used to annotate and interpret genetic variants and identify enriched pathways and gene ontology terms associated with the gene list. The review identified 77 articles that met the inclusion criteria. These articles provided information on 174 SNVs related to the MCL system that were linked to CVDs, T2D, or associated risk factors. The COMT gene was found to be significantly related to hypertension, dyslipidemia, insulin resistance, obesity, and drug abuse, with rs4680 being the most commonly reported variant. This systematic review found a strong association between the MCL system and the risk of developing CVDs and T2D, suggesting that identifying genetic variations related to this system could help with disease prevention and treatment strategies.

Dopaminergic pathway polymorphisms and heroin addiction: further support for association of CSNK1E variants

BACKGROUND & AIM

The dopaminergic pathways have been implicated in the etiology of drug addictions. The aim of this study was to determine if variants in dopaminergic genes are associated with heroin addiction.

MATERIALS & METHODS

The study includes 828 former heroin addicts and 232 healthy controls, of predominantly European ancestry. Ninety seven SNPs (13 genes) were analyzed.

RESULTS

Nine nominally significant associations were observed at CSNK1E, ANKK1, DRD2 and DRD3.

CONCLUSION

The results support our previous report of association of CSNK1E SNP rs1534891 with protection from heroin addiction. CSNK1E interacts with circadian rhythms and DARPP-32 and has been implicated in negative regulation of sensitivity to opioids in rodents. It may be a target for drug addiction treatment. Original submitted 8 August 2014; Revision submitted 8 October 2014.

Overlapping dopaminergic pathway genetic susceptibility to heroin and cocaine addictions in African Americans

Drugs of abuse activate the mesolimbic dopaminergic pathway. Genetic variations in the dopaminergic system may contribute to drug addiction. Several processes are shared between cocaine and heroin addictions but some neurobiological mechanisms may be specific. This study examined the association of 98 single nucleotide polymorphisms in 13 dopamine-related genes with heroin addiction (OD) and/or cocaine addiction (CD) in a sample of 801 African Americans (315 subjects with OD ± CD, 279 subjects with CD, and 207 controls). Single-marker analyses provided nominally significant evidence for associations of 24 SNPs) in DRD1, ANKK1/DRD2, DRD3, DRD5, DBH, DDC, COMT and CSNK1E. A DRD2 7-SNPs haplotype that includes SNPs rs1075650 and rs2283265, which were shown to alter D2S/D2L splicing, was indicated in both addictions. The Met allele of the functional COMT Val158Met was associated with protection from OD. None of the signals remained significant after correction for multiple testing. The study results are in accordance with the results of previous studies, including our report of association of DRD1 SNP rs5326 with OD. The findings suggest the presence of an overlap in genetic susceptibility for OD and CD, as well as shared and distinct susceptibility for OD in subjects of African and European descent.

Association between DRD2/ANKK1 TaqIA polymorphism and common illicit drug dependence: evidence from a meta-analysis

BACKGROUND

Growing evidence indicated conflicting results about the dopamine receptor D2 (DRD2)/kinase domain containing 1 gene (ANKK1) TaqIA single nucleotide polymorphism (rs1800497) and common illicit drug dependence risk including stimulants, opioid and marijuana. We conducted a meta-analysis to evaluate the association between the polymorphism and common illicit drug dependence risk.

METHOD

A total of 25 available studies (26 subgroups) testing the association between the polymorphism and common illicit drug dependence were examined through Oct 2013. Pooled odds ratios (ORs) and 95% confidence intervals (CI) were estimated using fixed- and random-effects models when appropriate. Heterogeneity and publication bias were evaluated.

RESULTS

We found the DRD2/ANKK1 TaqIA polymorphism was significantly associated with increased risk of opioid dependence under homozygote, dominant, and recessive genetic model, respectively (homozygote: OR=1.546, 95%CI=1.279-1.87; dominant: OR=1.265, 95%CI=1.055-1.516; recessive: OR=1.409, 95%CI=1.182-1.680). Subgroup analyses were similar to the results of the total population by ethnicity and quality score. Besides, we also found that Caucasian and low-quality studies were major sources of heterogeneity for opioid dependence. We failed to find any significant association between the polymorphism and stimulants or marijuana neither in total population nor subgroup analyses under any genetic model.

CONCLUSIONS

The current meta-analysis suggested that DRD2/ANKK1 TaqIA polymorphism might be associated with opioid dependence risk, but not associated with stimulants or marijuana dependence.

HIV-related cognitive impairment shows bi-directional association with dopamine receptor DRD1 and DRD2 polymorphisms in substance-dependent and substance-independent populations

It has been postulated that drugs of abuse act synergistically with HIV, leading to increased neurotoxicity and neurocognitive impairment. The CNS impacts of HIV and drug use converge on the mesocorticolimbic dopamine (DA) system, which contains two main receptor subtypes: dopamine receptors 1 (DRD1) and 2 (DRD2). DRD1 and DRD2 have been linked to substance dependence; whether they predict HIV-associated neurocognitive disorder (HAND) is unclear. Using an advanced-stage HIV+ population, we sought to determine if drug dependence impacts the contribution of DA receptor polymorphisms on neurocognition. We observed that both DRD1 and DRD2 polymorphisms were associated with opiate and cocaine dependence (P < 0.05) in Caucasian subjects, but not African-American individuals. Using linear regression analysis, we examined the polymorphisms for associations with neuropsychological performance in global and cognitive domain T-scores (Motor, Processing Speed, Verbal Fluency, Learning, Memory, Executive Functioning, Working Memory) while controlling for opiate and cocaine dependency. In the Motor domain, we observed an association for two DRD2 polymorphisms (P < 0.05) in Caucasian subjects. The effects differed for substance dependence groups as the direction of the correlations with DRD2 were opposite to what was seen in subjects without these dependencies. In African-American subjects, associations were observed in nearly every domain, and again, the direction of the correlation differed between substance-dependent and substance-independent groups. We conclude that studies to examine genetic risk for HAND must carefully account for substance dependence patterns when assaying dopaminergic systems, as the neurobiological substrates of cognition in HIV populations may vary with tonic alterations secondary to chronic substance exposures.

Exploring whether genetic differences between siblings explain sibling differences in criminal justice outcomes

Research has revealed that despite many similarities, siblings raised within the same household have also been found to be markedly different from one another. Behavioral differences between siblings have been primarily attributed to differential exposure to a wide variety of environmental influences. The potential role that between-sibling genetic differences play in the development of behavioral differences has been overlooked in the extant literature. The current study examines the association between differences in three dopaminergic polymorphisms (DAT1, DRD2, and DRD4) and differences in arrest, incarceration, and multiple arrests between siblings. Between-sibling difference scores were estimated for each examined polymorphism and each criminal justice outcome measure (along with all controls). Ordinary least squares (OLS) regression models were estimated to examine the potential association between genetic differences between siblings and differences in experiences within the criminal justice system. Models were estimated for the full sample and then for the same-sex male and female subsamples separately. The results provide preliminary evidence that between-sibling differences in some of the examined dopaminergic polymorphisms are associated with differences in contact with the criminal justice system. Findings are discussed in more detail and suggestions for future research are also provided.

Genetic variations in COMT and DRD2 modulate attentional bias for affective facial expressions

Studies have revealed that catechol-O-methyltransferase (COMT) and dopaminegic receptor2 (DRD2) modulate human attention bias for palatable food or tobacco. However, the existing evidence about the modulations of COMT and DRD2 on attentional bias for facial expressions was still limited. In the study, 650 college students were genotyped with regard to COMT Val158Met and DRD2 TaqI A polymorphisms, and the attentional bias for facial expressions was assessed using the spatial cueing task. The results indicated that COMT Val158Met underpinned the individual difference in attentional bias for negative emotional expressions (P = 0.03) and the Met carriers showed more engagement bias for negative expressions than the Val/Val homozygote. On the contrary, DRD2 TaqIA underpinned the individual difference in attentional bias for positive expressions (P = 0.003) and individuals with TT genotype showed much more engagement bias for positive expressions than the individuals with CC genotype. Moreover, the two genes exerted significant interactions on the engagements for negative and positive expressions (P = 0.046, P = 0.005). These findings suggest that the individual differences in the attentional bias for emotional expressions are partially underpinned by the genetic polymorphisms in COMT and DRD2.

Dopamine receptor D1 and postsynaptic density gene variants associate with opiate abuse and striatal expression levels

Opioid drugs are highly addictive and their abuse has a strong genetic load. Dopamine-glutamate interactions are hypothesized to be important for regulating neural systems central for addiction vulnerability. Balanced dopamine-glutamate interaction is mediated through several functional associations, including a physical link between discs, large homolog 4 (Drosophila) (DLG4, PSD-95) and dopamine receptor 1 (DRD1) within the postsynaptic density to regulate DRD1 trafficking. To address whether genetic associations with heroin abuse exist in relation to dopamine and glutamate and their potential interactions, we evaluated single-nucleotide polymorphisms of key genes within these systems in three populations of opiate abusers and controls, totaling 489 individuals from Europe and the United States. Despite significant differences in racial makeup of the separate samples, polymorphisms of DRD1 and DLG4 were found to be associated with opiate abuse. In addition, a strong gene-gene interaction between homer 1 homolog (Drosophila) (HOMER1) and DRD1 was predicted to occur in Caucasian subjects. This interaction was further analyzed by evaluating DRD1 genotype in relation to HOMER1b/c protein expression in postmortem tissue from a subset of Caucasian subjects. DRD1 rs265973 genotype correlated with HOMER1b/c levels in the striatum, but not cortex or amygdala; the correlation was inversed in opiate abusers as compared with controls. Cumulatively, these results support the hypothesis that there may be significant, genetically influenced interactions between glutamatergic and dopaminergic pathways in opiate abusers.

The ADH1B and DRD2 gene polymorphism may modify the protective effect of the ALDH2 gene against heroin dependence

Understanding the influences of genes involved in dopamine and serotonin metabolism, such as the aldehyde dehydrogenase 2 (ALDH2) and alcohol dehydrogenase 1B (ADH1B) genes, is critical for understanding addictive behavior. In addition, dopamine D2 receptor (DRD2) gene may also interact with the dopamine metabolizing genes and link to addiction. Therefore, we investigated the association between the ALDH2, ADH1B and DRD2 polymorphisms and heroin dependence. Heroin-dependent Han Chinese patients (n=304) and healthy controls (n=335) were recruited. Genotypes of ALDH2, ADH1B and DRD2 polymorphisms were analyzed using a polymerase chain reaction with restriction fragment length polymorphism. The frequency of the ALDH2*1/*1 genotype was significantly lower in heroin-dependent patients than in controls, but the frequency of ADH1B and DRD2 genotypes was not significantly different. Further stratification of the ALDH2 gene with the ADH1B gene showed that the protective effect of ALDH2*1/*1 existed only in patients who also carried the ADH1B*1/*1 and ADH1B*1/*2 genotype. Logistic regression analysis showed a significant interaction between ALDH2 and ADH1B (P=0.022) and DRD2, ALDH2 and ADH1B in patients (P=0.037). The ALDH2*1/*1, ADH1B*1/*1, and ADH1B*1/*2 genotypes may interact and protect their carriers against heroin dependence and the protective effect may be varied by the DRD2 gene polymorphism. We conclude that the protective effect of the ALDH2 polymorphism against heroin dependence may be modified by the ADH1B and DRD2 polymorphism.

ANKK1, TTC12, and NCAM1 polymorphisms and heroin dependence: importance of considering drug exposure

CONTEXT

The genetic contribution to liability for opioid dependence is well established; identification of the responsible genes has proved challenging.

OBJECTIVE

To examine association of 1430 candidate gene single-nucleotide polymorphisms (SNPs) with heroin dependence, reporting here only the 71 SNPs in the chromosome 11 gene cluster (NCAM1, TTC12, ANKK1, DRD2) that include the strongest observed associations.

DESIGN

Case-control genetic association study that included 2 control groups (lacking an established optimal control group).

SETTING

Semistructured psychiatric interviews.

PARTICIPANTS

A total of 1459 Australian cases ascertained from opioid replacement therapy clinics, 531 neighborhood controls ascertained from economically disadvantaged areas near opioid replacement therapy clinics, and 1495 unrelated Australian Twin Registry controls not dependent on alcohol or illicit drugs selected from a twin and family sample.

MAIN OUTCOME MEASURE

Lifetime heroin dependence.

RESULTS

Comparison of cases with Australian Twin Registry controls found minimal evidence of association for all chromosome 11 cluster SNPs (P ≥ .01); a similar comparison with neighborhood controls revealed greater differences (P ≥ 1.8 × 10(-4)). Comparing cases (n = 1459) with the subgroup of neighborhood controls not dependent on illicit drugs (n = 340), 3 SNPs were significantly associated (correcting for multiple testing): ANKK1 SNP rs877138 (most strongly associated; odds ratio = 1.59; 95% CI, 1.32-1.92; P = 9.7 × 10(-7)), ANKK1 SNP rs4938013, and TTC12 SNP rs7130431. A similar pattern of association was observed when comparing illicit drug-dependent (n = 191) and nondependent (n = 340) neighborhood controls, suggesting that liability likely extends to nonopioid illicit drug dependence. Aggregate heroin dependence risk associated with 2 SNPs, rs877138 and rs4492854 (located in NCAM1), varied more than 4-fold (P = 2.7 × 10(-9) for the risk-associated linear trend).

CONCLUSIONS

Our results provide further evidence of association for chromosome 11 gene cluster SNPs with substance dependence, including extension of liability to illicit drug dependence. Our findings highlight the necessity of considering drug exposure history when selecting control groups for genetic investigations of illicit drug dependence.

Possible association between human blood types and opioid addiction

Drug addiction is a complex disorder that has been shown to have a genetic component like several other diseases. Finding any factor that is associated with higher risk of addiction tendency may influence the strategies of prevention and treatment of drug abuse and also provide an avenue of further research in genetics, immunology, and other related fields. This case-control study aimed at finding the frequency rate of ABO blood groups and Rhesus (Rh) factor among opioid dependents. Therefore, 249 opioid dependents referred to the Drug Quit center at Bam, Iran (case group) were compared with 360 blood donors referred to the Blood Transfusion Center (control group) in regard to the frequency of blood groups and Rh factor. The two groups were matched for demographic features. The odds ratio for AB blood group in addicts was 3.98 compared to non-addicts (p < .001) and the odds ratio of negative Rh in addicts compared to non-addicts was 4.27 (p < .001). According to the findings, in this population the frequency of negative Rh and AB blood group were significantly less than the predictive values. The relationship between opioid use and blood group type requires a cohort study eliminating all extraneous factors in order to be proved.

Can the chronic administration of the combination of buprenorphine and naloxone block dopaminergic activity causing anti-reward and relapse potential?

Opiate addiction is associated with many adverse health and social harms, fatal overdose, infectious disease transmission, elevated health care costs, public disorder, and crime. Although community-based addiction treatment programs continue to reduce the harms of opiate addiction with narcotic substitution therapy such as methadone maintenance, there remains a need to find a substance that not only blocks opiate-type receptors (mu, delta, etc.) but also provides agonistic activity; hence, the impetus arose for the development of a combination of narcotic antagonism and mu receptor agonist therapy. After three decades of extensive research, the federal Drug Abuse Treatment Act 2000 (DATA) opened a window of opportunity for patients with addiction disorders by providing increased access to options for treatment. DATA allows physicians who complete a brief specialty-training course to become certified to prescribe buprenorphine and buprenorphine/naloxone (Subutex, Suboxone) for treatment of patients with opioid dependence. Clinical studies indicate that buprenorphine maintenance is as effective as methadone maintenance in retaining patients in substance abuse treatment and in reducing illicit opioid use. With that stated, we must consider the long-term benefits or potential toxicity attributed to Subutex or Suboxone. We describe a mechanism whereby chronic blockade of opiate receptors, in spite of only partial opiate agonist action, may ultimately block dopaminergic activity causing anti-reward and relapse potential. While the direct comparison is not as yet available, toxicity to buprenorphine can be found in the scientific literature. In considering our cautionary note in this commentary, we are cognizant that, to date, this is what we have available, and until such a time when the real magic bullet is discovered, we will have to endure. However, more than anything else this commentary should at least encourage the development of thoughtful new strategies to target the specific brain regions responsible for relapse prevention.

Association between polymorphisms of DRD2 and DRD4 and opioid dependence: evidence from the current studies

Several studies have assessed the association between genetic polymorphisms of DRD2 and DRD4 genes and opioid dependence risk, while the results were inconsistent. We performed a meta-analysis, including 6,846 opioid dependence cases and 4,187 controls from 22 individual studies, to evaluate the roles of four variants (DRD2 -141ins/delC, rs1799732; DRD2 311 Ser > Cys, rs1801028; DRD2-related TaqI A, rs1800497 and DRD4 exon III VNTR) in opioid dependence for the first time. We found that the -141delC polymorphism was significantly associated with increased risk of opioid dependence (homozygote comparison: odds ratios [OR], 2.71; 95% confidence interval [CI], 1.74-4.22; dominant comparison: OR, 1.27; 95% CI, 1.09-1.48). Similarly, the TaqI A1 polymorphism was also significantly increased opioid dependence risk (homozygote comparison: OR, 2.06; 95% CI, 1.25-3.42; dominant comparison: OR, 1.34; 95% CI, 1.08-1.67). Moreover, long allele (≥5-repeat) and 7-repeat allele of DRD4 exon III VNTR were found to be associated with significantly increased opioid dependence risk (OR, 1.50; 95% CI, 1.24-1.80 and OR, 1.57; 95%, 1.18-2.09, respectively). However, no association was detected between the DRD2 311 Ser > Cys polymorphism and opioid dependence. In conclusion, our results suggested that DRD2 -141ins/delC, DRD2-related TaqI A and DRD4 exon III VNTR polymorphisms might play important roles in the development of opioid dependence.

Role of novelty seeking personality traits as mediator of the association between COMT and onset age of drug use in Chinese heroin dependent patients

BACKGROUND

Personality traits such as novelty seeking (NS) are associated with substance dependence but the mechanism underlying this association remains uncertain. Previous studies have focused on the role of the dopamine pathway.

OBJECTIVE

Examine the relationships between allelic variants of the catechol-O-methyltransferase (COMT) gene, NS personality traits, and age of onset of drug use in heroin-dependent subjects in China.

METHODS

The 478 heroin dependent subjects from four drug rehabilitation centers in Shanghai who were genotyped for eight tagging single nucleotide polymorphisms (SNP) on the COMT gene completed the NS subscale from the Temperament and Character Inventory. Multivariate analyses were used to assess the potential mediating role of NS personality traits in the association between COMT gene variants and the age of onset of heroin use.

PRINCIPAL FINDINGS AND CONCLUSIONS

In the univariate analysis the COMT rs737866 gene variants were independently associated with both NS and age of onset of drug use: those with the TT genotype had higher NS subscale scores and an earlier onset age of heroin use than individuals with CT or CC genotypes. In the multivariate analysis the inclusion of the NS subscore variable weakened the relationship between the COMT rs737866 TT genotype and an earlier age of onset of drug use. Our findings that COMT is associated with both NS personality traits and with the age of onset of heroin use helps to clarify the complex relationship between genetic and psychological factors in the development of substance abuse.

Shared brain vulnerabilities open the way for nonsubstance addictions: carving addiction at a new joint?

For more than half a century, since the beginning of formal diagnostics, our psychiatric nosology has compartmentalized the compulsive pursuit of substance (e.g., alcohol, cocaine, heroin, nicotine) from nonsubstance (e.g., gambling, food, sex) rewards. Emerging brain, behavioral, and genetic findings challenge this diagnostic boundary, pointing to shared vulnerabilities underlying the pathological pursuit of substance and nonsubstance rewards. Working groups for the fifth revision of the Diagnostic and Statistical Manual of Mental Disorders, fifth edition (DSM-V), are thus considering whether the nosologic boundaries of addiction should be redrawn to include nonsubstance disorders, such as gambling. This review discusses how neurobiological data from problem gambling, obesity, and "normal" states of attachment (romantic infatuation, sexual attraction, maternal bonds) may help us in the task of carving addictions "at a new joint." Diagnostic recarving may have a positive effect on addiction research, stimulating discovery of "crossover" pharmacotherapies with benefit for both substance and nonsubstance addictions.

Gender effect on association between DRD2 polymorphism and substance dependence in a Spanish sample

Our aim was to examine a possible association between substance dependence and the TaqIA polymorphism of the D2 dopamine receptor (DRD2), a single nucleotide polymorphism (SNP) located at the 3' UTR region of the DRD2 gene. A case-control design stratified by gender was used to analyze the genotypes of this SNP in a sample of 125 substance-dependent patients according to DSM-IV and 203 blood donors recruited as controls in two general city hospitals in Madrid, Spain. Genomic DNA from peripheral blood samples was amplified through PCR to identify the variants of the SNP in the DRD2 gene. Analyses performed with Chi(2) tests revealed that the A1 allele (A1/A1 and A1/A2 genotypes) of the Taq 1A SNP of the DRD2 gene was significantly associated with substance dependence in males, but not in the whole sample. Male patients had significantly higher rates of the A1-containing genotypes than male controls. The finding of an association between substance dependence and the DRD2 gene TaqIA SNP only in males suggests the existence of gender-specific differences in the genetic underpinnings of substance dependence.

Genetics of dopamine receptors and drug addiction: a comprehensive review

Drug dependence is a chronic, relapsing disorder in which compulsive drug-seeking and drug-taking behaviours persist despite serious negative consequences. Addictive substances, such as opioids, ethanol, psychostimulants and nicotine, induce pleasant states or relieve distress, effects that contribute to their recreational use. Dopamine is critically involved in drug addiction processes. However, the role of the various dopaminergic receptor subtypes has been difficult to delineate. Here, we will review the information collected implicating the receptors of the D1 family (DRD1 and DRD5) and of the D2 family (DRD2, DRD3 and DRD4) in drug addiction. We will summarize the distribution of these receptors in the brain, the preclinical experiments carried out with pharmacological and transgenic approaches and the genetic studies carried out linking genetic variants of these receptors to drug addiction phenotypes. A meta-analysis of the studies carried out evaluating DRD2 and alcohol dependence is also provided, which indicates a significant association. Overall, this review indicates that different aspects of the addiction phenotype are critically influenced by dopaminergic receptors and that variants of those genes seem to influence some addiction phenotypes in humans.

Haplotypic variants in DRD2, ANKK1, TTC12, and NCAM1 are associated with comorbid alcohol and drug dependence

BACKGROUND

Each gene in the chromosome 11q23 cluster of NCAM1, TTC12, ANKK1, and DRD2 is functionally linked to dopamine in brain. Many association studies of DRD2 and substance dependence (SD), including alcohol dependence (AD) and drug dependence (DD), have been reported; the results have been inconsistent. Recent association studies have considered this cluster more comprehensively, examining the association of SD with several risk variants mapped to the other genes in the cluster. Because comorbid AD with DD (AD+DD) is common, we hypothesized that heterogeneity of the SD diagnoses studied might have contributed to the inconsistency of prior results.

METHODS

We conducted 2 separate association studies of AD+DD and AD without DD (AD-only) in 1,090 European-Americans using family-based and case-control designs and 43 single nucleotide polymorphisms mapped to this cluster. We used a generalized linear model and haplotype score tests for the case-control sample, and the family-based association test for the family sample.

RESULTS

For AD+DD, the risk regions centered on TTC12 exon 3 [optimal individual haplotype simulated p (p(oihs)) = 0.000015], and another extended from ANKK1 exon 8 to DRD2;C957T (p(oihs) = 0.0028), in both samples. NCAM1 exon 12 markers showed global significance in both designs, but were significant for specific haplotypes (p(oihs) = 0.0029) only for the family sample. For AD-only, NCAM1 intron 14 to 18 and the junction of ANKK1 and DRD2 were associated globally. Population stratification was excluded as the basis for these results. Linkage disequilibrium contrast tests supported selection at TTC12 exon 3 and ANKK1 exon 2.

CONCLUSIONS

We conclude that variants in TTC12 exon 3, NCAM1 exon 12, and the two 3'-ends of ANKK1 and DRD2 co-regulate risk for comorbid AD and DD.

Activation instead of blocking mesolimbic dopaminergic reward circuitry is a preferred modality in the long term treatment of reward deficiency syndrome (RDS): a commentary

Background and hypothesis

Based on neurochemical and genetic evidence, we suggest that both prevention and treatment of multiple addictions, such as dependence to alcohol, nicotine and glucose, should involve a biphasic approach. Thus, acute treatment should consist of preferential blocking of postsynaptic Nucleus Accumbens (NAc) dopamine receptors (D1-D5), whereas long term activation of the mesolimbic dopaminergic system should involve activation and/or release of Dopamine (DA) at the NAc site. Failure to do so will result in abnormal mood, behavior and potential suicide ideation. Individuals possessing a paucity of serotonergic and/or dopaminergic receptors, and an increased rate of synaptic DA catabolism due to high catabolic genotype of the COMT gene, are predisposed to self-medicating any substance or behavior that will activate DA release, including alcohol, opiates, psychostimulants, nicotine, gambling, sex, and even excessive internet gaming. Acute utilization of these substances and/or stimulatory behaviors induces a feeling of well being. Unfortunately, sustained and prolonged abuse leads to a toxic" pseudo feeling" of well being resulting in tolerance and disease or discomfort. Thus, a reduced number of DA receptors, due to carrying the DRD2 A1 allelic genotype, results in excessive craving behavior; whereas a normal or sufficient amount of DA receptors results in low craving behavior. In terms of preventing substance abuse, one goal would be to induce a proliferation of DA D2 receptors in genetically prone individuals. While in vivo experiments using a typical D2 receptor agonist induce down regulation, experiments in vitro have shown that constant stimulation of the DA receptor system via a known D2 agonist results in significant proliferation of D2 receptors in spite of genetic antecedents. In essence, D2 receptor stimulation signals negative feedback mechanisms in the mesolimbic system to induce mRNA expression causing proliferation of D2 receptors.

Proposal and conclusion

The authors propose that D2 receptor stimulation can be accomplished via the use of Synapatmine™, a natural but therapeutic nutraceutical formulation that potentially induces DA release, causing the same induction of D2-directed mRNA and thus proliferation of D2 receptors in the human. This proliferation of D2 receptors in turn will induce the attenuation of craving behavior. In fact as mentioned earlier, this model has been proven in research showing DNA-directed compensatory overexpression (a form of gene therapy) of the DRD2 receptors, resulting in a significant reduction in alcohol craving behavior in alcohol preferring rodents. Utilizing natural dopaminergic repletion therapy to promote long term dopaminergic activation will ultimately lead to a common, safe and effective modality to treat Reward Deficiency Syndrome (RDS) behaviors including Substance Use Disorders (SUD), Attention Deficit Hyperactivity Disorder (ADHD), Obesity and other reward deficient aberrant behaviors. This concept is further supported by the more comprehensive understanding of the role of dopamine in the NAc as a "wanting" messenger in the meso-limbic DA system.

Association of dopamine and opioid receptor genetic polymorphisms with response to methadone maintenance treatment

BACKGROUND

Genetic variations of the dopamine and opioid receptors could influence the response to methadone maintenance treatment (MMT).

METHODS

We included 238 MMT patients according to their response to treatment and methadone dosing, along with 217 subjects without substance dependence. All were genotyped for polymorphisms of the dopamine D1, D2, micro-opioid and delta-opioid receptor genes.

RESULTS

The polymorphisms of the micro-opioid (118A>G), delta-opioid (921T>C), dopamine D1 (DdeI) and D2 (TaqI A) receptor genes were not associated with response to MMT and methadone dosing, whereas an association was found with the dopamine D2 receptor (DRD2) 957C>T polymorphism. The 957CC carriers were more frequently non-responders to treatment (OR=2.4; p=0.02) and presented a fourfold shorter period of negative urine screening (p=0.02). No significant differences in allele frequencies were observed between the MMT patients and the control group, suggesting no association of the analyzed polymorphisms with opioid dependence.

CONCLUSIONS

These results suggest that DRD2 genotype may contribute to the understanding of the interindividual variability to the response to MMT.

A preliminary study: novelty seeking, frontal executive function, and dopamine receptor (D2) TaqI A gene polymorphism in patients with methamphetamine dependence

INTRODUCTION

Dopamine receptor polymorphisms have been associated with specific patterns of novelty seeking (NS) temperamental nature and frontal executive function. In addition, carriers of dopamine receptor type 2 (DRD2)-TaqI A1 have been hypothesized to be potentially vulnerable to addictive behaviors. In the present study, the association between dopamine D2 polymorphisms, NS, and frontal executive function was studied.

METHODS

Thirty-seven methamphetamine (MA)-dependent subjects and 40 healthy comparison subjects participated in the current study. The severity of addiction, NS temperament, and frontal executive functions were measured using the Addiction Severity Index, the NS subscale in the Temperament and Character Inventory, and the Wisconsin Card Sorting Test, respectively. All subjects were genotyped with regard to DRD2-TaqI polymorphisms.

RESULTS

The prevalence of DRD2-TaqI A1 allele polymorphisms was greater in the MA-abuser group than in the comparison group. Patients with MA dependence also had higher NS characteristics and high scores in total trials, errors, and perseverative errors of the Wisconsin Card Sorting Test than comparison subjects. Within patients with MA dependence, the subgroup of DRD2-TaqI A1 carrier had greater NS scores relative to those without, whereas there was only a trend level of lower frontal executive function in the first subgroup.

CONCLUSION

In the present study, the MA-dependent patients with DRD2-TaqI A1 allele had significantly greater NS scores and lower frontal executive function with a trend level than those without. These preliminary results suggest that MA-dependent patients may have the possibility of genetic and biogenic vulnerability to MA.

Acute opiate overdose in Tehran: the forgotten role of opium

INTRODUCTION

The global epidemic of opiate use continues to spread and is an increasing burden especially in developing countries. Acute opiate overdose (AOO) is one of the most dramatic complications of drug abuse. The purpose of this study is to examine the epidemiology of acute opiate overdose in a poisoning center in Tehran.

METHODS

In this cross-sectional survey, patients who attended the emergency room of Loghman-Hakim hospital - the only poisoning center in Tehran - and diagnosed with acute opiate overdose over a six month period were included.

RESULTS

Overdose was more common among men (91.2%). The mean and standard deviation of age was 36.9+/-15. The most frequent opiate agent was opium (56.5%) followed by heroin. Opium was most commonly used by regular users, as a single agent and through ingestion. Benzodiazepines, antidepressants and alcohol were the most common agents consumed accompanied with opiates. The mortality rate was 8.8% which was not significantly different between cases of heroin and opium overdose.

CONCLUSION

Opium was the major cause of overdose in our study. This result suggests that opium is not a harmless form of addiction although it is regarded as a thing of the past in many countries.

Allelic and genotypic associations of DRD2 TaqI A polymorphism with heroin dependence in Spanish subjects: a case control study

Background

Conflicting associations with heroin dependence have been found involving the A1 allele of dopamine D2 receptor gene (DRD2) TaqI A polymorphism.

Methods

We compared two samples of unrelated Spanish individuals, all of European origin: 281 methadone-maintained heroin-dependent patients (207 males and 74 females) who frequently used non-opioid substances, and 145 control subjects (98 males and 47 females).

Results

The A1-A1 genotype was detected in 7.1% of patients and 1.4% of controls (P = 0.011, odds ratio = 5.48, 95% CI 1.26–23.78). Although the A1 allele was not associated with heroin dependence in the entire sample, the frequency of A1 allele was higher in male patients than in male controls (24.4% vs. 16.3%, P = 0.024, odds ratio = 1.65, 95% CI 1.07–2.57). A logistic regression analysis showed an interaction between DRD2 alleles and gender (odds ratio = 1.77, 95% CI 1.15–2.70).

Conclusion

Our results indicate that, in Spanish individuals, genotypes of the DRD2 TaqI A polymorphism contribute to variations in the risk of heroin dependence, while single alleles contribute only in males.

Nucleus accumbens D2/3 receptors predict trait impulsivity and cocaine reinforcement

Stimulant addiction is often linked to excessive risk taking, sensation seeking, and impulsivity, but in ways that are poorly understood. We report here that a form of impulsivity in rats predicts high rates of intravenous cocaine self-administration and is associated with changes in dopamine (DA) function before drug exposure. Using positron emission tomography, we demonstrated that D2/3 receptor availability is significantly reduced in the nucleus accumbens of impulsive rats that were never exposed to cocaine and that such effects are independent of DA release. These data demonstrate that trait impulsivity predicts cocaine reinforcement and that D2 receptor dysfunction in abstinent cocaine addicts may, in part, be determined by premorbid influences.

Perspectives on current directions in the neurobiology of addiction disorders relevant to genetic risk factors

There is a significant heritability of drug addiction disorders, but potential genes that may underlie such vulnerability have not been clearly identified. Common neurobiological candidates for drug abuse include genes related to dopamine, opioid neuropeptide, and glutamate transmission that play important roles in drug reward and inhibitory control. This article provides an overview of genetic polymorphisms linked to these neurobiological systems, particularly in relation to psychostimulant- and opioid-addiction vulnerability.

The effect of dopamine D2, D5 receptor and transporter (SLC6A3) polymorphisms on the cue-elicited heroin craving in Chinese

Heroin dependence is resulted from the interaction between multiple genetic and environmental factors. Subjective craving is considered to be a central phenomenon, which contributes to the continuation of drug use in active abuser and the occurrence of relapse in detoxified abusers. Dopamine pathway has been implicated in the cue-elicited craving for a variety of addictive substances. The objective of this study was to test the hypothesis that heroin addicts carrying specific variants in dopamine-related genes would have higher levels of craving following exposure to a heroin-related cue. Craving induced by a series of exposure to heroin-related cue was assessed in a cohort of Chinese heroin abuser (n = 420) recruited from natural abstinence center at Shanghai. Significantly stronger cue-elicited heroin craving was found in individuals carrying D2 dopamine receptor gene (DRD2) TaqI RFLP A1 allele than the non-carriers (P < 0.001). Furthermore, we did not observed significant association of cue-elicited craving with the nine-repeat allelic variants in dopamine transporter gene (DAT) SLC6A3 and with the dinucleotide repeat polymorphism (DRP) 148bp allele in D5 dopamine receptor gene (DRD5). The results of our study suggest that human dopamine pathway be involved in cue-induced heroin craving, and indicate a potential genetic risk factor for persistent heroin behavior and relapse.